The major objectives of the project are to delineate the roles in the host-parasite relationship of unusual surface components of pathogenic mycobacteria, principally of M. tuberculosis. The interests currently embrace studies on the mycobacterial sulfatides, other potentially strongly acidic lipids and mycobacterial trehalose glycolipids in general, all of which appear potentially to have some role in pathogenesis. Further, among a series of some 40 wild type patient strains of M. tuberculosis from the Indian subcontinent, a specific aromatic phthiocerol mycocerosate is elaborated only by the "attenuated" strains in the group. For many of these substances we seek to determine distribution, chemical structures, how they might contribute to pathogenicity (or attenuation) and to assess possible immunogenic potential. Several mycobacterial trehalose glycolipids act synergistically with cord factor (6,6' dimycoloyl trehalose) to enhance the notable toxicity of the latter. The principal sulfolipid (SL-I) of M. tuberculosis, strain H37Rv and its desulfated product are particularly effective. They may also act synergistically in tumor-suppressive activity. The complete structure of SL-I has been established, along with that of a minor sulfatide (SL-III) and of the Attenuation Indicator lipid. We continue an interest in the role of mycobacterial lipids as receptor-site substances for mycobacteriophages.